1. Field of the Invention
The present invention relates to a lens barrel for holding a lens, and more particularly, relates to a lens barrel for holding a lens in which a lens mounted in the lens barrel can be adjusted in relation to decentering readily with a simple construction.
2. Description Related to the Prior Art
There are various optical instruments such as a liquid crystal projector including an optical system. A lens apparatus in the optical system is constituted by a combination of various lenses. A plurality of types of lens barrels contain the lenses, and include stationary and movable barrels. The movable barrel contains a component of the lenses for focusing or zooming, and is movable in the optical axis direction. The stationary barrel contains a component of the lenses which is stationary on the optical instrument having the lens apparatus.
As the lens apparatus is obtained by assembling the lens barrels, the lens must be positioned exactly in the lens barrels before intended optical performance can be acquired. This is important particularly if the lens has a high power or operates for correcting aberration. It is known in the art to adjust the lens by finely shifting in a plane perpendicular to an optical axis before securing on the lens barrel. An example of this is disclosed in JP-A 2003-131104.
In JP-A 2003-131104, three projections are formed on the periphery of the lens. A tool for adjustment is used to push the projections after mounting the lens in the lens barrel for adjusting parallel decentering. This requires molding the lens together with the projections. However, there is a problem in irregularity in flow or resin in the vicinity of the projections in the course of injection of resin into molds. Also, distortion may occur in an optical surface due to influence of a sink mark or shrink mark of the resin. The disclosed method in the known document is disadvantageous in view of optical performance.
In FIG. 4, a through hole 3a is formed in a barrel body 3 of a lens holding barrel or lens barrel 2 at each of three points which rotationally divide the circumference equally. An external adjusting rod or pin 4 is moved through the through hole 3a in and out to adjust a lens 5 in relation to parallel decentering. After this, the adjusting rod 4 is removed. Adhesive agent is introduced through the through hole 3a to attach the lens 5 on the barrel body 3 by adhesion. For the adjustment, a receiving surface 6 of the inside of the lens barrel 2 must be pressed on the lower surface of the lens 5 for keeping an orientation perpendicular to the optical axis. To this end, a weighting device 7 in a ring shape is placed on the lens 5. An auxiliary lens 9 is incorporated in a platen or surface table 10. The lens barrel 2 is positioned on the surface table 10, is subjected to application of a laser beam S. A CCD or area sensor 12 receives incidence of the laser beam S. The adjusting rod 4 is moved at an adjusted amount so as to set a position of incidence of the laser beam S at the home position of the CCD 12, so as to adjust the lens 5 in relation to parallel decentering.
Furthermore, a use of clip shaped spring 15 of FIG. 5 is known in place of the weighting device 7. The clip shaped spring 15 keeps the lens 5 pressed on the receiving surface 6. The adjusting rod 4 is moved into and out of the through hole 3a to adjust the lens 5 in relation to parallel decentering. Note that the lens barrel 2 in FIG. 5 is set on the platen or surface table 10 in an orientation reverse to that of FIG. 4. However, the lens barrel 2 can be oriented in the same manner as that of FIG. 4.
According to JP-A 2003-131104 or FIGS. 4 and 5, it is important to move the lens in parallel with the receiving surface while the lens is pressed suitably on the receiving surface. In the method of JP-A 2003-131104, an adjuster as a tool causes a projection to press the lens on the receiving surface, at the same time as the lens is moved in parallel with the receiving surface. However, a shortcoming lies in unwanted forming of the projection on the lens integrally. In FIG. 4 or 5, a problem lies in a combined use of the weighting device 7 or the clip shaped spring 15. If force of biasing of the clip shaped spring 15 becomes weak with time, it is difficult to press the lens 5 on the receiving surface 6 in a well balanced condition.